Ultrasound operates by creating an image from sound in three steps—producing a sound wave, receiving echoes, and interpreting those echoes to create an image.
Ultrasound has many uses in medical applications. For example, ultrasound is routinely used during pregnancy to provide images of the fetus in the womb. Generally, a water-based gel is applied to the patient's skin, and a hand-held probe, called an ultrasound transducer, is placed directly on and moved over the patient. The probe typically contains one or a plurality of piezoelectric elements that vibrates and generates a sound wave when a current is applied. In ultrasound devices, the sound wave is typically produced by creating short, strong vibrational pulses using the piezoelectric transducer element. The sound wave is reflected (echoes) from tissues and structures and returns an echo, which vibrates the transducer elements and turns the vibration into electrical pulses. The electrical pulses are then sent to a processor and then to an ultrasound scanner having a display where they are transformed into a viewable analog or digital image on the display. Ultrasound contrast agents (which may be introduced into the blood) are known for enhancing visibility of blood vessels so that smooth needles, sheaths or tools may avoid inadvertent puncture of a vessel. Surrounding human tissue of blood vessels of interest in a particular medical procedure or blood flow may be seen in an ultrasound image. Also, methods for improving the surface echogenicity of tools are known which permit, for example, improved reflection of sound waves back to the ultrasound transducer assembly.
While general-purpose ultrasound machines may be used for most imaging purposes, certain procedures require specialized apparatus. For example, in a pelvic ultrasound, organs of the pelvic region can be imaged using either external or internal ultrasound devices used together or in combination with ultrasound image guided catheters of the present invention (implanted or inserted, for example, via the rectal opening, the mouth, a vein or other useable openings to a human body). In contrast, echocardiography, which is used in cardiac procedures, can require specialized machines to take into account the dynamic nature of the heart.
Ultrasound has advantages over other imaging methods such as magnetic resonance imaging (MRI) and computed tomography (CT) or optical coherence tomography (OCT), but these, along with known X-ray imaging can be used together to gather displayed images of a patient's region of interest. Ultrasound produces a sequence of images in real time and so, for example, a mother may see the ultrasound image of her baby and see the baby's heartbeat. Also, ultrasound is relatively inexpensive compared to techniques such as MRI and CT. Ultrasound also is capable of imaging muscle and soft tissue very well, can delineate interfaces between solid and fluid filled spaces (for example, for cardiocentesis procedures with a pericardial sac), and may show the structure of organs and their internal components (such as a heart valve). Ultrasound renders live images in real time in sequence and can be used, for example, to view blood vessels in relation to the operation of organs in real time (with or without contrast). Ultrasound has no known long-term side effects and generally causes little to no discomfort to a patient. Further, ultrasound equipment is widely available, flexible and portable.
However, ultrasound does have some drawbacks. When used on obese patients, image quality is compromised as the overlying adipose tissue scatters the sound and the sound waves are required to travel greater depths, resulting in signal weakening (attenuation) on transmission and reflection back to the ultrasound transducer (especially a surface-mounted ultrasound system). Even in non-obese patients, depth penetration is limited, thereby making it difficult to obtain images of structures located deep within the body. Further, ultrasound has trouble penetrating bone and, thus, for example, ultrasound imaging of the brain within skull bone is limited from external to animal bone. Ultrasound also does not perform well when there is gas present (as in the gastrointestinal tract and lungs). Still further, a highly skilled and experienced ultrasound operator is necessary to obtain quality images. These drawbacks do not, however, limit the usefulness of ultrasound as a medical diagnostic and treatment tool.
The use of ultrasonic apparatus for imaging areas of the human body, either alone or in combination with other instruments, is known, for example, for guiding therapeutic instruments through a catheter to a field of view within a human body. For example, ultrasound devices have been combined with catheters for insertion into a body, usually through a vein or artery, to reach a part of the human body for examination or treatment. Such devices are commonly known in the art as “imaging catheters.”
For example, U.S. Pat. No. 5,704,361 to Seward et al. discloses a volumetric image ultrasound transducer underfluid catheter system. For example, FIGS. 2-9 and 11-12 of Seward et al. and their attendant description suggest specific methods of intervention for imaging purposes in the vicinity of a human heart. To reach such an area of interest within a human body, an ultrasound imaging and hemodynamic catheter may be advanced via the superior vena cava to a tricuspid valve annulus. A distal end of a cylindrical body includes a guide wire access port and a guide wire provides a means of assuring that the catheter reaches a target for imaging. A surgical tool may be fed through the catheter to the area imaged.
U.S. Pat. No. 6,572,551 to Smith et al. provides another example of an imaging catheter. Tools such as a suction device, guide wire, or an ablation electrode, may be incorporated in an exemplary catheter according to Smith et al.
U.S. Pat. No. 5,967,984 to Chu et al. describes an ultrasound imaging catheter with a cutting element which may be an electrode wire or a laser fiber. FIGS. 1 and 2 of Chu et al. also describe a balloon 14 and a means to inflate the balloon. The balloon, for example, may be utilized to dilate a vessel having strictures imaged via the imaging catheter.
Other imaging catheters are known. For example, U.S. Pat. No. 6,162,179 to Moore teaches bending (using a pull wire) an acoustic window into a known and repeatable arc for improved three-dimensional imaging. U.S. Pat. No. 6,306,097 to Park et al. discloses an intravascular ultrasound imaging catheter whereby a first lumen provides access for an ultrasound imaging catheter and a second lumen provides a working port for a tool. U.S. Pat. No. 5,505,088 to Chandraratna et al. teaches using a 200 MHz transducer in an ultrasonic microscope combined with a catheter as a delivery means for the microscope to provide imaging of myocardial tissue. According to Chandraratna et al., lower frequency ultrasound transducers can provide deeper penetration in the tissue but do not provide the image quality provided by higher frequencies.
Optical coherence tomography (OCT) operates in a similar manner to ultrasound in producing an image having high resolution but the transmitted light signal reaches only so far into human tissue. White light diodes covering the visible spectrum may be used to transmit light through, for example, a transparent window to the human tissue, and the echo is received and passed to a display which may create a three-dimensional image. Near infrared and other radio frequencies, visible and invisible, may be applied to create an image of human tissue at, for example, a site of a medical procedure.
Needle guides are known for probes and catheters. Typically, a needle guide may be located at the top of the probe or catheter and provide a channel having a diameter for a specific needle size. The needle may be inserted subcutaneously with or without imaging by sliding the needle from the surgeon end through the needle channel. Also, the needle guide is in one piece and incapable of being opened to release the needle from the probe or catheter. The needle is removed by pulling the needle through the needle channel toward the surgeon end, and the needle may capture debris or fluid such as blood at the needle channel tip as the needle is pulled out of the needle channel.
All the above-cited references are incorporated by reference as to any description which may be deemed essential to an understanding of illustrated and discussed aspects and embodiments of devices and methods herein and as summarized below.